test(applets): add GTest unit tests for dde-apps classes (54 tests) - #1707

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/setup-go@v3. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Include file: <QSignalSpy> not found. Please note: Cppcheck does not need standard library headers to get proper results.

Include file: <QStringList> not found. Please note: Cppcheck does not need standard library headers to get proper results.

Include file: <QString> not found. Please note: Cppcheck does not need standard library headers to get proper results.

Include file: <QSet> not found. Please note: Cppcheck does not need standard library headers to get proper results.

Include file: <gtest/gtest.h> not found. Please note: Cppcheck does not need standard library headers to get proper results.

Include file: "categoryutils.h" not found.

Include file: <QStringList> not found. Please note: Cppcheck does not need standard library headers to get proper results.

Include file: <QString> not found. Please note: Cppcheck does not need standard library headers to get proper results.

Include file: <QList> not found. Please note: Cppcheck does not need standard library headers to get proper results.